99 ram stalling

Have a 99 dodge ram 1500 V8 5.2
Wife says it has been stalling usually after idling in the parking lots picking kids up from school. Sometimes when stopped, sometimes while driving home at a decent speed. Gives no warning, just turns off. Had it to a mechanic several times he can't find a problem because it won't stall when he runs it, or when I drive it. No codes showing, she says engine light only comes on when it dies. It will usually start back up immediately or after a few minutes. Doesn't do this everyday, sometimes once a week, once every few weeks or sometimes it stalls several times in a day.
Has new plugs, wires..IAC valve, PCV valve, Ignition Coil

Any suggestions are appreciated